Method of insulating a ship&#39;s propeller for minimizing electrolytic action



July 18, 1961 J, HQQD, JRh T 2,992,961

METHOD OF INSU I PRO LER FOR MINIMIZI E TROL C AC Original Filed June 29, 1956 Sheets-Sheet 1 BY ,3. .4. Law;

ATTORNEY July 18, 1961 J. c. HOOD, JR. ET AL I 2,992,951

METHOD OF INSULATING A SHIPS PROPELLER FOR MINIMIZING ELECTROLYTIC ACTION 29, 1956 2 Sheets-Sheet 2 Original Filed June INVENTORS JAMES C. HOOD, JR-

HERMAN S. PREISER BY A? 4. 26M? ATTORNEY 2 Claims. (Cl. 154-128) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for govenmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to insulating sleeves and more particularly to a plastic laminate sleeve used in the electrical isolation of metallic parts forming a galvanic circuit in the propelling apparatus of a marine tvessel and a method of applying the same to said appara- This application is a divisional application of application Serial No. 595,029, filed June 29, 1956, now Patent No. 2,892,503, June 30, 1959, which latter application was a continuation-in-part of the applicants then copending application Serial No. 490,709, filed on February 25, 1955, now abandoned entitled, Plastic Sleeve for Electrically Isolating Marine Propellers.

The naval and merchant fleets have been confronted with a serious problem of corrosion of shafting, struts, rudders and stern areas of vessels, and this problem has become acute becaue of the modern practice of utilizing metals of different types in these areas of the vessel. This disease of deterioration can be traced to two prime sources of infection; namely, cavitation defects at the stern and galvanic corrosion currents existing between the bronze propeller members and the steel members comprising the hull and the shafting.

The concept of preventing electrolytic action by breaking a galvanic circuit is old. The prior art discloses use of insulating bushings between a rotary shaft and a metallic housing for the bushings which support the rotating shaft. The bushings eliminate electrolytic action occurring between the shaft and bearing in which sea water serves as an electrolyte for completing the circuit.

This invention is directed to and eliminates the problem of galvanic corrosion associated with the propeller hub, shafting and stem of a ship. It is accomplished by isolating the propeller hub and attached blades from the shaft by interposing an insulating material between the hub and shaft taper. This insulating material consists of a plastic member which serves to remove the large cathodic area of the propeller from the steel shaft and hull system (anodic areas) thereby reducing the galvanic corrosion normally taking place between these parts.

It is therefore an object of the invention to provide a plastic insulator for insulating contacting metals in an electrolyte.

Another object of the invention is the provision of a plastic sleeve for isolating a propeller and blades from the shaft and other stern parts of a ship.

Still another object of the invention is the provision of a plastic sleeve for electrically isolating a propeller hub and blades from a keyed shaft and other stern parts of a ship.

A further object of the invention is the provision of a plastic sleeve for prohibiting galvanic corrosion of a hull and other stern components of a ship in metallic contact with the more noble propeller.

Patent f A still further object of the invention is the provision 2,992,961 Patented July 18, 1961 of a sleeve of molded glass cloth laminated material serving as an insulator between a propeller hub and shaft and for providing ease of assembly in mounting the hub on the propeller shaft.

An additional object is to provide a simple and inexpensive method of applying an electrically insulating sleeve to the propeller shaft of a ship so as to electrically insulate said shaft from a propeller mounted thereon.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a view in elevation, partly in section, showing the position of a plastic sleeve relative to a propeller hub and tapered shaft;

FIG. 2 is a view taken on line 2--2 of FIG. 1 showing the arrangement of the palstic sleeve in a keyway formed in the propeller shaft-body;

FIG. 3 is a view showing a modification of the sleeve shown in FIG 2.;

FIG. 4 is a sectional view showing a modification of the sleeve and key shown in FIGS. 2 and 3;

FIG. 5 is a perspective view, showing a preliminary stage of assembly, of a modification of the plastic sleeve, tapered shaft and propeller hub arrangement of FIGS. 14; and

FIG. 6 is a sectional view, in assembled form, of the structure shown in FIG. 5.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIGS. 1 and 2, a propeller shaft 10 provided with a reduced portion 12 tapering inwardly towards the end of the shaft. The shaft is provided with an extension 14 which is exteriorly threaded for receiving a nut 16 rigidly securing propeller hub 18 to the shaft. The hub is of the usual streamlined contour having openings extending around its periphery for receiving a plurality of blades 20 which are either fixed or rotatably mounted therein. Both the hub and the shaft are respectively provided with channel-like openings 22 and 24 which, when aligned, are adapted to receive a key 26 for preventing relative rotary movement of the hub on the shaft.

Interposed between the tapered end 12 and hub 18 for prohibiting galvanic corrosion is a thin sleeve of polyesterglass laminate 28. The insulation is made complete by a washer 30 composed of the same material, and bemg backed by a metallic disc 32 which prevents the plastic from tearing when the bolt 16 is tightened on the shaft. The laminate consists of from three to five layers of an .006.008" thick glass cloth, thoroughly impregnated with a thermosetting resin. The laminate sleeve is made in matched metal molds so as to be of uniform thickness and consistency in material.

It will be noted that the modification of FIG. 2 shows the type of sleeve that is molded with a keyway adapted for fitting the channel formed in shaft 10. When this type of sleeve is used, the parts are assembled by placing the sleeve on the tapered shaft so that the channel of the sleeve snugly fits the keyway provided in the shaft. Key 26 is inserted therein and the propeller hub subsequently pressed on the tapered end of the shaft with pressures of in the neighborhood 30,000 p.s.i. Washer 30 and nut 16 are then attached for completing the assemblying operation.

The modification of FIG. 3 is similar to that of FIG. 2 with the exception that the sleeve is molded in such fashion to lit the keyway provided in hub 13. In this construction, the sleeve is molded around the metal key so as to make fitting of the sleeve and key into position an integrated operation.

The modification of FIG. 4 is similar to that of FIGS. 2 and 3 with the exception that the insulating sleeve 28 is of a size such that it covers the portion of the shaft 10 which is adapted to be overlaid by hub 18, but minus the keyway lining portion shown in the modifications of FIGS. 2 and 3. The sleeve 28' instead of being completely tubular, is provided with a logitudinally extending slot of the same width as keyways 30 and 32 in the shaft and propeller hub respectively, and adapted to coincide therewith in the manner shown.

The key 26 is insulated from the adjacent walls of the respective keyways 30 and 32 by means of a plastic sleeve 34 of either the same or similar material as sleeve 28', and adapted to fit within both keyways 30 and 32 in the manner shown in FIG. 4. In this construction the hub is assembled on the shaft, with the respective keyways in alignment, and the keyway insulator sleeve 30 is placed within said keyways, as shown; the key 26 is then placed within the sleeve 34 and driven into place. This modification, as can be seen in FIG. 4, serves to completely electrically insulate the shaft 10 from the hub 18, and also the key 26 from both the shaft and the hub.

The modification shown in FIGS. and 6 differs from those described above in that the insulating sleeve is formed directly on the shaft in a manner hereinafter described, instead of being pre-molded.

The method for forming the modification of FIGS. 5 and 6 is known as the Wet-lay-up method, and consists of applying a coating of thermosetting resin 36 to the tapered portion of a shaft 10 and the keyway formed therein, followed by the application of a proper size layer of glass fabric 38 on the top of the resin; the combination is then subjected to heat sufiicient to cause the resin to set and thereby hold the glass fabric on the shaft. It is pointed out that either a polyester or an epoxy resin may be used.

One example of a suitable resin mixture comprises an epoxy resin, such as bisphenol-epichlorohydrine plastic compound, combined with a suitable hardener such as either an amine or an acid type catalyst system, said mixture also containing a small amount of poly-sulfide rubber compound. Listed below are a number of commercially available epoxy resins along with their accompanying hardening agents:

Epoxy resin: Hardener Shell Epon 828---- Diethylene triamine. Ciba 502 Piperidine (acid type catalyst).

Hysol ERL 2774 Hysol ZZL 0803.

The following is an example of an epoxy resin mixture used in carrying out the applicants method; the proportions are by weight:

Percent Epoxy resin-Hysol ERL 2774 62 HardenerHysol ZZL 0803 33 Thiokol (polysulfide rubber compound)LP3 5 (1) Mixture of ethylene glycol and either maleic acid or anhydride (2) Mixture of ethylene glycol and either phthallic acid or anhydride Polyester resins of the above type are available under the following trade names:

Marco 28-C Laminac 4110 Selectron 503 One method of applying an insulating sleeve to nonkeyed propeller shaft in accordance with this invention consists of the following steps:

(1) The propeller hub and shaft are roughened with, for example, an aloxite cloth, and then cleaned with a solvent.

(2) A thin coat 36 of epoxy resin, m'med in the proportions set forth above, is applied to the shaft and hub and then cured with heat lamps.

(3) After suitable setting period, a single layer of glass cloth 38, for example, style 181, finish Volan A, is out to fit the tapered section of a shaft. Another coat of resin is applied to the shaft, and the glass cloth is set in the resin, the cloth being Worked by hand to free entrapped air and to insure a good fit. The resin is again cured with heat lamps or the like.

(4) After the resin has thoroughly hardened, the overlapping glass fabric seam, if any, is sanded smooth.

(5) Both the shaft and the hub are again coated with epoxy resin and the two parts are assembled; the as sembly is heated for 36 hours by infra-red heat lamps, or the like, and a suitable interval is allowed for the resin to set, after which the assembly is ready for use.

In applying an insulating sleeve to a keyed shaft, the same steps are followed, with these modifications: After step No. 4, the shaft and keyway provided therein are machined to proper dimensions, following which step 5 is carried out, with the keyway in the hub, and the key itself being resin coated.

In applying this method to a keyed shaft, the key 26' and respective keyways are provided with a modified double-tapered construction with rounded edges to permit easy driving without damage to the plastic sleeve. See FIG. 5.

It is pointed out that conventional propellers in use today require a keyed, tapered mechanical connection between the propeller hub and tail shaft. The key is necessary to insure foolproof mechanical linkage between propeller and shaft. The existence of this key and keyway makes it extremely difiicult to electrically isolate the propeller from its shaft and still maintain foolproof mechanical linkage. This invention teaches the use of a laminated plastic sleeve for insulating a keyed shaft from a propeller hub and a method for applying the same to said shaft.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A method of electrically insulating a propeller shaft, having a tapered end portion and having a keyway formed in said end portion, from a propeller hub mounted on and fixed relative to said tapered end portion by a key, said tapered end portion and hub being made of different metals, comprising the steps of applying a first coat of thermosetting resin to said tapered portion of the shaft including the walls of said keyway in the shaft, setting said resin by heat, applying a second coat of thermosetting resin over said first coat, applying a layer of glass cloth to said tapered portion of the shaft, including the wall portions of said keyway, over said second coat of resin so as to completely surround said shaft and cover the walls of said keyway, setting said second coat of resin by heat, coating the glass cloth with a layer of thermosetting resin, coating the interior of the propeller hub and the external surfaces of said key with said resin and assemblying said propeller hub and key on said shaft, heating the assembly to cause thermosetting of said last coats of resin, thereby resin bonding said hub to said glass cloth, key and shaft.

2. A method of electrically insulating a propeller shaft having a tapered end portion, having a keyway formed therein, from a propeller hub mounted on and fixed to said tapered end portion by a key, said tapered end portion and hub being of ditferent metals; comprising the steps of applying a first coat of thermosetting resin to the tapered end portion of said shaft and the Walls of said keyway, setting said resin by heat, applying a second coat of thermosetting resin over said first coat, applying a layer of glass cloth to said tapered end portion of said shaft, including the walls of said keyway, over said second coat of resin so as to surround the tapered end portion of said shaft, setting said second coat of resin by 10 heat; machining the cloth covered tapered end portion of the shaft and said keyway to predetermined dimensions, coating the glass cloth with a layer of thermosetting resin, coating the interior of the propeller hub and the surfaces of said key with said thermosetting resin; assemblying said propeller hub and key on said shaft, heating the assembly to cause setting of said last coats of resin, thereby resin bonding said hub to said cloth covered shaft and said key.

References Cited in the file of this patent UNITED STATES PATENTS 2,270,583 Forton Ian. 20, 1942 2,404,904 Collins July 30, 1946 2,650,185 Larson Aug. 25, 1953 

2. A METHOD OF ELECTRICALLY INSLUATING A PROPELLER SHAFT HAVING A TAPERED END PORTION, HAVING A KEYWAY FORMED THEREIN, FROM A PROPELLER HUB MOUNTED ON FIXED TO SAID TAPERED END PORTION BY A KEY, SAID TAPERED END PORTION AND HUB BEING OF DIFFERENT METALS, COMPRISING THE STEPS OF APPLYING A FIRST COAT OF THERMOSETTING RESIN TO THE TAPERED END PORTION OF SAID SHAFT AND THE WALLS OF SAID KEYWAY, SETTING SAID RESIN BY HEAT, APPLYING A SECOND COAT OF THERMOSETTING RESIN OVER SAID FIRST COAT, APPLYING A LAYER OF GLASS CLOTH TO SAID TAPERED END PORTION OF SAID SHAFT, INCLUDING THE WALLS OF SAID KEYWAY, OVER SIAD SECOND COAT OF RESIN SO AS TO SURROUND THE TAPERED END PORTION OF SAID SHAFT, SETTING SAID SECOND COAT OF RESIN BY HEAT, MACHINING THE CLOTH COVERED TAPERED END PORTION OF THE SHAFT AND SAID KEYWAY TO PREDETERMINED DIMENSIONS, COATING THE GLASS CLOTH WITH A LAYER A THERMOSETTING RESIN, COATING THE INTERIOR OF THE PROPELLER HUB AND THE SURFACES OF SAID KEY WITH SAID THERMOSETTING RESIN, ASSEMBLYING SAID PROPELLER HUB AND KEY ON SAID SHAFT, HEATING THE ASSEMBLY TO CAUSE SETTING OF SAID LAST COATS OF RESIN, THEREBY RESIN BONDING SAID HUB TO SAID CLOTH COVERED SHAFT AND SAID KEY. 